So, I think it's common knowledge by now that there's a layer of Venus's atmosphere just above the sulfuric acid clouds at about 1 ATM pressure with a temperature of slightly above 0°C. By my understanding the only barrier to habitability is the fact that that layer is composed primarily of CO2. Now, this alone is sufficient for inflatable colonies filled with air, perhaps even with balconies if you were to wear a good winter coat and a air mask. What if, however, we used airborne photosynthetic bacteria to terraform just this layer of Venus? It seems to be a much more feasible undertaking than total terraforming, and best of all, it isn't a prerequisite to colonization, that is, you can already have colonies there and terraform over time while people are already living there.

So, are there any problems I missed? Also, how large a quantity of bacteria would be necessary? Other requisite resources? General thoughts?

Mixing is going to be pretty darn rapid. With the kind of winds that Venus has, any oxygen produced is going to suffuse out into the surrounding layers with astonishing rapidity. Plus, it's not just a matter of adding oxygen; carbon dioxide will kill you in half an hour if it's over 10% concentration, so you'd have to have another gas in the atmosphere that's not toxic.

And while you could definitely walk out onto the balcony for a few minutes with a warm coat and a breathing apparatus, those levels of carbon dioxide will burn the crap out of your eyes and ears (not to mention nose and throat if exposed). There would also probably be CO2 toxicity problems with skin absorption after a while.

Now, if you could get a layer of non-toxic gas that is lighter than carbon dioxide but heavier than oxygen, it could theoretically be used to form a "buffer layer" between the toxic carbon dioxide "sea" and the breathable oxygen "atmosphere". Though that might also have suffusion problems unless it had some kind of intermolecular attraction to itself that resisted mixing. But of course 100% oxygen is also toxic over extended periods, so you'd either need your buffer gas to taper off in concentration with increasing altitude so that it would have about 70% concentration at the 1 atm altitude, or you'd need to add a third gas to mix with the oxygen.

sevenperforce wrote:And while you could definitely walk out onto the balcony for a few minutes with a warm coat and a breathing apparatus, those levels of carbon dioxide will burn the crap out of your eyes and ears (not to mention nose and throat if exposed). There would also probably be CO2 toxicity problems with skin absorption after a while.

You might need more than that. Cutaneous respiration in humans contributes only 1-2% (at most) of our body's total oxygen needs, but it's responsible for the majority of the oxygen needs of our skin...at least the outer layers, that is. This study determined that the respiratory needs of the outer 0.25-0.4 mm of our skin is supplied almost exclusively by external atmospheric oxygen. So prolonged exposure to a 100% CO2 environment would very likely result in acidosis and cell death in the outer layers of our skin, causing a "leathering" effect as a thin layer of scar tissue began to cover the entire body. Can't imagine that would be good.

Dead bacteria that go uneaten would gradully settle out of the atmosphere at ground level, creating a sediment layer, analogous to how dead plankton accumulate on the sea floor if nothing eats them.

As for the issue of whether it would combust in the high temperatures of the surface, there would have to be a fairly large buildup of oxygen at low altitudes before such combustion could even be possible. Given that carbon dioxide is the primary greenhouse gas in the Venusian atmosphere, the amount of carbon removal that would already have taken place by that point may be sufficient to reduce surface temperatures from the current 800-odd Farenheit (450 C) to below the nearly-500 Farenheit (275 C) necessary for ignition.

Neil_Boekend wrote:They don't have a high terminal velocity in the Venusian atmosphere.

I was referring to the high ambient temperature on Venus's surface.

As for the issue of whether it would combust in the high temperatures of the surface, there would have to be a fairly large buildup of oxygen at low altitudes before such combustion could even be possible. Given that carbon dioxide is the primary greenhouse gas in the Venusian atmosphere, the amount of carbon removal that would already have taken place by that point may be sufficient to reduce surface temperatures from the current 800-odd Farenheit (450 C) to below the nearly-500 Farenheit (275 C) necessary for ignition.

We also don't need to just worry about reactions that resemble fire, but those that resemble rusting. At 450 C it would take (wild guess, but probably high) a bacteria a millisecond to burn at Earth's oxygen pressure. Reduce the partial pressure to 1 millionth? It burns up in 20 minutes now; proportionately longer, but not enough time to do much.

The thing about recursion problems is that they tend to contain other recursion problems.

Neil_Boekend wrote:..... I would not expect this to be a fast process..

Do you expect the mixing to be hundreds of millions of times slower than photosynthesis? I understand there to be a lot of convection on Venus and I wouldn't have guessed it'd take more than a matter of days for a non-trivial fraction of the oxygen to switch levels.

It's also worth pointing out that the troposphere cooling involves reducing the greenhouse effect AND convection. The gas at the solid surface can only cool down in so far as it contacts (directly or indirectly) the gas at the optical surface.

.... even with 20% oxygen in the upper layers.

That's not very far along in the terraforming process. 99% of Venus' atmosphere is the troposphere, so that's wouldn't significantly affect the surface temperature.20% O2 at the 1 ATM level isn't sufficient to breath the air there either. Carbon dioxide is toxic.

The thing about recursion problems is that they tend to contain other recursion problems.

Neil_Boekend wrote:..... I would not expect this to be a fast process..

Do you expect the mixing to be hundreds of millions of times slower than photosynthesis? I understand there to be a lot of convection on Venus and I wouldn't have guessed it'd take more than a matter of days for a non-trivial fraction of the oxygen to switch levels.

I was under the impression that the upper and the lower atmosphere had vastly different chemical compositions. Dunno where I got it, I can't find it now. Due to wind speeds I think I imagined it.

Steal a proton from carbon? That would make Boron, which is even more toxic than carbon. Nitrogen is toxic as well at above 400 or so kilopascals, causing nitrogen narcosis. The only gas that could be used as a buffer to make a human-breathable mixture at Venus surface pressure is helium.